The 1-hydroxy epimers of chloramphenicol and thiamphenicol formed from the reduction of the respective 1-oxo derivatives with (3H) NaBH4 have been separated preparatively by high pressure liquid chromatography on a microns Bondapak C1, column. This separation procedure permits the facile and rapid preparation of the (1-3H) labeled derivatives of chloramphenicol and its analogues.